Heads-up: Potentially breaking changes to the GDK drawing model pushed

["Jasper St. Pierre" <jstpierre mecheye net>]

To better support Wayland with fewer copies and less drawing artifacts, I've pushed some potentially breaking changes to GDK, namely around gdk_cairo_create and gdk_window_begin_paint_region.

https://git.gnome.org/browse/gtk+/commit/?id=d48adf9cee7e340acd7f8b9a5f9716695352b848
https://git.gnome.org/browse/gtk+/commit/?id=be30e440c350f0f3e0f2572f7f3eab54ef96af0e

With these changes, it is now illegal to call gdk_cairo_create outside of a begin_paint / end_paint. This was always sketchy, and would never work on Wayland anyway. If your code does this, we will print a warning and return a dummy surface which won't ever be composited back into the main surface.

Additionally, it is now forbidden to call gdk_window_begin_paint_region more than once. Previously, the code had a "paint stack" which tracked paints, but since GTK+ never used this codepath it was never actually tested and was indeed broken on Wayland due to the way the Wayland backend was written. Again, we will print a warning in this case and return.

As part of these changes, gtk_widget_set_double_buffered was deprecated and removed. Again, it will never work on Wayland, as that is natively double-buffered, and it would simply break there.

I tested with some local big applications like Ardour and the GNOME applications, but don't have a GTK+3 build of Firefox, LibreOffice, Eclipse, or any big GTK+ apps like Inkscape or The GIMP.

Please double-check to make sure your apps still work fine. If you have a problem with any of this or I broke your apps by accident, please reply and I'll try to fix it.

Thanks!

--
  Jasper